1. Field of the Invention
The present invention relates, in general, to methods and systems for cooling processors (e.g., central processing units or CPUs) in servers and other computing devices, and, more particularly, to methods, assemblies, and components for mounting heat sinks in desired heat transfer contact with a CPU while allowing for manufacturing tolerances and for stresses and/or forces applied to the heat sink during shipping and operation of the computing device.
2. Relevant Background
Removal of heat has become one of the most important challenges facing computer designers as failure to adequately cool devices can cause failure or operating problems. The rate of power dissipation from electronics components such as from processors (or CPUs) in high-performance server units continues to increase. In most cases, air cooling is used to remove heat from a heat generating surface of a CPU, a motherboard, and other components of the server or other computer/electronic product, with each chassis or box containing the heat generating components including one or more fans that draw air into the chassis or box to provide cooling and allow continued operation of the components. To improve heat removal, a heat sink may be mounted in contact with a top surface of the CPU such that the amount of surface area for transferring heat to the flowing air is increased.
For example, FIG. 1 illustrates a partial sectional view of a server (or other computer system) 100 that is designed to use forced-air cooling with a heat sink 140. The server 100 includes a housing or chassis 110 with a base plate or support element 114 supporting a motherboard or board 120. A CPU 130 is positioned upon the board 120, such as a high capacity processor that generates significant amounts of heat. A heat sink 140 is placed over the CPU 130 with a base 142 in contact with the upper surface of the CPU 130 to allow heat to be transferred to the heat sink 140. Air is forced to flow through the fins 148 of the heat sink 140 to remove heat. The heat sink 140 is attached to the base plate or support element with fasteners 150 and springs 156 providing a primary mount of the heat sink 140 to the chassis 110. To provide more surface area, it is generally desirable to increase the number and height of the fins 148, but the height and other dimensions of the heat sink 140 are limited by the configuration of the chassis 110 and other components in chassis 110. As a result, computer designs often include relatively long heat sinks 140, e.g., 200 to 300 millimeters in length (or width). The primary mounting with fasteners 150 is typically centered on the heat sink 140, and a significant amount of the heat sink 140 may be unsupported or overhanging as shown by the length of the overhang, Loverhang, in FIG. 1. For example, the overhang. Loverhang, for some recent heat sink designs has been over 100 millimeters on both sides of the heat sink 140 relative to the supporting fasteners 150 or other supports such as mounting plates or the like. The heat sinks 140 are generally formed of metal such as copper, and the overhanging portion may be relatively heavy, such as several pounds.
Providing mechanical restraints in the mounting of a CPU heat sink, such as heat sink 140, is often a challenge to designers. Designers not only have to try to control forces but also deal with tolerances in mating or interconnected parts (e.g., stresses may be created when components are assembled due to tolerance stack up and the like). In general as shown in FIG. 1, springs are provided in the primary mount of the heat sink to try to control dynamic forces and potential assembly tolerances issues. The primary mount provides controlled static loading to the CPU, including allowance for dynamic loads and tolerances. In such an arrangement, other points of contact with the heat sink are avoided to prevent compromising operation of the spring elements.
In the case of large overhanging portions of a heat sink (e.g., as found in very wide/long and low profile designs), shock and vibration loading is often not well controlled by existing designs. As shown in FIG. 1, the heat sink is supported in a cantilevered manner, which may result in significant forces being applied to the heat sink and/or upon the CPU/support structure as the ends of the heat sink 140 move up and down as shown with arrow 160, with degradation of the thermal interface material (TIM) interface being an important failure mechanism. Rigid attachments are sometimes used to support the ends of the heat sink, but the overhanging portion acts as an effective lever in transmitting forces applied by these rigid restraints to the CPU or its attachments (e.g., assembly of the rigid restraint often applies a downward force upon the end of the heat sink that is transferred or leveraged to the CPU or sink primary mount) and/or causes thermal degradation of the operation of the heat sink.
Hence, there remains a need for enhanced heat sink mounting designs to address issues with overhanging portions of the heat sink. Preferably such heat sink mounts would be adapted to augment, and not replace, primary mounts such as the spring mounts shown in FIG. 1 (e.g., not to withstand main forces but instead to handle forces experienced at or input by the overhanging portion). Further, it may be desirable for the heat sink mounts to address dynamic loading that may occur during shipping such as shock loads if the server is dropped or moved quickly and/or during operations that cause vibrations of the heat sink, which may impart significant forces upon the cantilevered sink (e.g., vibrations at or near resonance may rapidly damage the computing device or its components).